A new book on Uber by Fortune's Adam Lashinsky is coming out soon, but Bloomberg has revealed one juicy anecdote ahead of time. CEO Travis Kalanick reportedly called up Tesla CEO Elon Musk to propose a partnership on self-driving cars, but Musk rebuffed the offer and even tried to talk him out of it.

"I said, 'Look man, we should partner,' " Kalanick stated in the book. "Elon spent the rest of the call convincing me that it's too far out, and it's not realistic, that I should just stick to what we do best and be focused, or I'm going to fuck it all up. That's when I knew Tesla was competing."

Kalanick wasn't aware that Tesla was already working on autonomous vehicle tech, even though it had unveiled its "Autopilot" driving assistant hardware. Shortly afterwards, Musk detailed a master plan for self-driving Tesla cars, including an autonomous ride-hailing service that would directly compete with Uber. Tesla has done perhaps the most impressive fully autonomous demo yet, steering a car from a customer's house to Tesla offices and parking without any human intervention.

Uber, meanwhile, has been mired in problems. It was sued by Google's Waymo self-driving division for intellectual property theft and now risks a criminal prosecution. On top of that, it recently demoted self-driving lead Anthony Levandowski, who was subsequently barred by a judge from working on any projects involving crucial LIDAR tech.

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